I. Field of the Invention
The present invention relates to the fields of oncology, genetics and molecular biology. More particular the invention relates to the identification, on human chromosome 10, of a tumor suppressor gene. Defects in this gene are associated with the development of cancers, such as gliomas.
II. Related Art
Oncogenesis was described by Foulds (1958) as a multistep biological process, which is presently known to occur by the accumulation of genetic damage. On a molecular level, the multistep process of tumorigenesis involves the disruption of both positive and negative regulatory effectors (Weinberg, 1989). The molecular basis for human colon carcinomas has been postulated, by Vogelstein and coworkers (1990), to involve a number of oncogenes, tumor suppressor genes and repair genes. Similarly, defects leading to the development of retinoblastoma have been linked to another tumor suppressor gene (Lee et al., 1987). Still other oncogenes and tumor suppressors have been identified in a variety of other malignancies. Unfortunately, there remains an inadequate number of treatable cancers, and the effects of cancer are catastrophic--over half a million deaths per year in the United States alone.
One example of the devastating nature of cancer involves tumors arising from cells of the astrocytic lineage are the most common primary tumors of the central nervous system (Russell & Rubinstein, 1989). The majority of these tumors occur in the adult population. Primary brain tumors also account for the most common solid cancer in the pediatric patient population and the second leading cause of cancer deaths in children younger than 15 years of age. An estimated 18,500 new cases of primary brain tumors were diagnosed in 1994 (Boring et al., 1994). Epidemiological studies show that the incidence of brain tumors is increasing and represents the third most common cause of cancer death among 18 to 35 year old patients. Due to their location within the brain and the typical infiltration of tumor cells into the surrounding tissue, successful therapeutic intervention for primary brain tumors often is limited. Unfortunately, about two-thirds of these afflicted individuals will succumb to the disease within two years. The most common intracranial tumors in adults arise from cells of the glial lineage and occur at an approximately frequency of 48% glioblastoma multiforme (GBM), 21% astrocytomas (A) (anaplastic (AA) and low grade) and 9% ependymomas and oligodendrogliomas (Levin et al., 1993).
Genetic studies have implicated several genes, and their corresponding protein products, in the oncogenesis of primary brain tumors. Among the various reported alterations are: amplification of epidermal growth factor receptor and one of its ligands, transforming growth factor-alpha, N-myc; gli, altered splicing and expression of fibroblast growth factor receptors, and loss of function of p53, p16, Rb, neurofibromatosis genes 1 and 2, DCC, and putative tumor suppressor genes on chromosomes 4, 10, 17 (non-p53), 19, 22, and X (Wong et al., 1987; El-Azouzi et al., 1989; Nishi et al., 1991; James et al., 1988; Kamb et al., 1994; Henson et al., 1994; Yamaguchi et al., 1994; Bianchi et al., 1994; Ransom et al., 1992; Rasheed et al., 1992; Scheck and Coons, 1993; Von Demling et al., 1994; Rubio et al., 1994; Ritland et al., 1995).
The most frequent alterations include amplification of EGF-receptor (.about.40%), loss of function of p53 (.about.50%), p16 (.about.50%), Rb (.about.30%) and deletions on chromosome 10 (&gt;90%). Furthermore, the grade or degree of histological malignancy of astrocytic tumors correlates with increased accumulation of genetic damage similar to colon carcinoma. Moreover, some changes appear to be relatively lineage- or grade-specific. For instance, losses to chromosome 19q occur predominantly in oligodendrogliomas, while deletions to chromosome 10 and amplification and mutation of the EGF-receptor occur mainly in GBMs. The deletion of an entire copy or segments of chromosome 10 is strongly indicated as the most common genetic event associated with the most common form of primary brain tumors, GBMs.
Cytogenetic and later allelic deletion studies on GBMs clearly have demonstrated frequent and extensive molecular genetic alterations associated with chromosome 10 (Bigner et al., 1988; Ransom et al., 1992; Rasheed et al., 1992; James et al., 1988: Fujimoto et al., 1989; Fults et al., 1990, 1993; Karlbom et al., 1993; Rasheed et al., 1995; Sonoda et al, 1996; Albarosa et al., 1996). Cytogenetic analyses have clearly shown the alteration of chromosome 10 as a common occurrence in GBMs, with 60% of tumors exhibiting alteration. Allelic deletion studies of GBMs have also revealed very frequent allelic imbalances associated with chromosome 10 (90%). However, the losses are so extensive and frequent that no chromosomal sublocalization of a consistent loss could be unequivocally defined by these analyses.
Several recent studies have implicated the region 10q25-26, specifically a 17 cM region from D10S190 to D10S216. A telomeric region from D10S587 to D10S216 was implicated by allelic deletion analysis using a series of low and high grade gliomas that exhibited only a partial loss of chromosome 10 (Rasheed et al, 1995). This region (.about.1 cM) was lost or noninformative in 11 GBM's, 4 AA's, 1 A and 1 oligodendroglioma, suggesting localization of a candidate region. This study also illustrated that deletions to chromosome 10 occur in lower grade gliomas. Albarosa et al. (1996) suggest a centromeric candidate region based on a small allelic deletion in a pediatric brain tumor from the makers D10S221 to D10S209. Saya et al., using a series of GBMs, have suggested two common regions of deletions, 10q26 and 10q24 (D10S192).
The short arm of chromosome 10 also has been implicated to contain another tumor suppressor gene. Studies first provided functional evidence of a tumor suppressor gene on 10p in glioma (Steck et al, 1995) which was later shown for prostate (Sanchez et al., 1995; Murakami et al., 1996). The latter study has implicated a 11 cM region between D10S1172 and D10S527. Allelic deletion studies of gliomas have shown extensive deletion on 10p, but again, no firm localization has been achieved (Karlbom et al., 1993; Kimmelman et al., 1996; these regions of chromosome 10 are shown to FIG. 1, below). Furthermore, the amplification of EGF-receptor has also been shown to occur almost exclusively in tumors that had deletions in chromosome 10, suggesting a possible link between these genetic alterations (Von Deimling et al., 1992).
Deletions on the long arm, particularly 10q24, also have been reported for prostate, renal, uterine, small-cell lung, endometrial carcinomas, meningioma and acute T-cell leukemias (Carter et al., 1990; Morita et al, 1991; Herbst et al., 1984; Jones et al., 1994; Rempel et al., 1993; Peiffen et al., 1995; Petersen et al., 1997). Recently, detailed studies on prostate carcinoma have shown that (1) the short and long arm of chromosome 10 strongly appear to contain tumor suppressor genes, and (2) the localization of the long arm suppressor gene maps to the 10q23-24 boundary (Gray et al., 1995; Ittmann, 1996, Trybus et al., 1996). The region of common deletion identified by these three groups is centered around D10S215 and extends about 10 cM (FIG. 1). The region overlaps with our candidate region, however, no further localization within the region was reported fro prostate carcinoma. The allelic losses associated with prostate carcinoma also appear to occur in only about 30-40% of the tumors examined. Furthermore, deletions are observed in more advance staged tumors, similar to GBMs, and may be related to metastatic ability (Nihei et al., 1995; Komiya et al., 1996). The combination of these results suggest that multiple human cancers implicate the region 10q23-24.
Differences in locations of the candidate regions suggest several possibilities. First, the presence of two or more tumor suppressor genes on 10q are possible. Second, not all deletions may effect the tumor suppressor gene locus. These alternatives are not mutually exclusive. In support of the latter possibility, a potential latent centromere was suggested to occur at 10q25 which may give rise to genetic alterations, particularly breakage (Vouillaire et al., 1993).
Despite all of this information, the identity of the gene (or genes) involved with the 10q23-24-related tumor suppression remained elusive. Without identification of a specific gene and deduction of the protein for which it codes, it is impossible to begin developing an effective therapy targeting this product. Thus, it is an important goal to isolate the tumor suppressor(s) located in this region and determine its structure and function.